The clash of Washington visits this week is an irresistible story for the British press; but there is more to Pope Benedict's trip to the United States than the fact that it is crowding out Gordon Brown's local airtime. Compared to his predecessor, Benedict is a reluctant traveller. America's Catholics, moreover, make up only 6% of the Pope's worldwide flock. So it should be assumed that Benedict has crossed the Atlantic for a more compelling reason.

Part of that reason is surely that America's Catholics are, like the country they inhabit, disproportionately rich and influential. As such, they have unusual clout in making or marring the Pope's efforts to reaffirm the church's role. This Pope is a conservative. American Catholics, though far from doctrinally homogeneous, lean to the liberal end of the spectrum. A recent poll found 63% of US Catholics want same-sex couples to have the same rights as heterosexuals, while 62% think abortion should be legal in most or all cases. That makes them not just more liberal than the Vatican, but also more liberal than most Americans. The Pope wants to do what he can to change those views.

Before he can do that, however, he has to address the sex-abuse scandals that have cost the US Catholic church more than $2bn so far in legal fees and compensation settlements, leaving at least 5,000 known victims and bankrupting five US dioceses. That was why the Pope tried to get the issue out of the way before he arrived - to the outrage of victims who believe the church hierarchy is still in denial and cover-up mode. Significantly the Pope has left Boston, the centre of the storm, off his itinerary.

The Pope is well aware that he has arrived during a crucial election. America's 65 million Catholics are no more homogeneous politically than doctrinally. But they are certainly numerous. As many as one in every four voters is a Catholic - in Pennsylvania, where there is a key primary next week, the proportion is closer to one in three. Historically Democratic, in 2004 a majority of Catholics voted for George Bush. Democrats are working to win them back, but Benedict surely understands his power to put all the candidates on the spot.

Benedict-watchers believe that, while he admires American religiosity, he wishes it could be better harnessed. His speeches and sermons in America will be carefully watched for what they say not just about private but public morality. He gave nothing away in his White House remarks yesterday, but the list of hot topics stretches from stem cell research, abortion and immigration to Iraq, nuclear weapons, climate change and free-market capitalism. It is hard to believe he has come all this way to such a spotlit pulpit in order to say nothing of consequence.